Sand core coating composition



2,809,1 l7 Patented Oct. 8, 1957 SAND CORE COATING COMPOSITION Ernest L. Waterhouse, Vassar, and Lawrence L. Zinsmeister, Saginaw, Mich., assignors to Eaton Manufactllll'ing Company, Cleveland, Ohio, a corporation of No Drawing. Application March 10, 1953, Serial No. 341,596

5 Claims. (Cl. 106-3828) This invention relates to founding and more particularly to improved Wash or coating compositions for cores for use primarily in gray iron or alloy steel casting in permanent molds. This invention constitutes a continuation in part of their application Serial No. 297,575, filed July 7, 1952, Patent Number 2,786,771, granted March 26, 1957.

It has been determined essentially necessary in the casting of gray iron or alloy steel articles using permanent cast iron molds in conjunction with dry sand cores to provide an effective coating of the cores so as to eliminate burn-on or surface roughness in the surface of the casting as it contacts the core. This burn-on is apparently due to the tendency of the gases, which are generated during the casting operation to penetrate the sand core and carry the molten metal into the surface of the core whereby a rough surface is obtained on the casting.

Broadly the invention comprehends the provision of a wash or coating composition for sand cores which eliminates surface roughness from permanent mold cast gray iron or alloy steel casting.

Among the other principal objects of the invention is the provision of a sand core coating composition, that a. May be applied with a spray gun if desired;

b. Is harmless and non-toxic;

c. In its dry state is resilient, resists abrasion, and will not rub, peel or flake off;

d. Is fast drying;

e. Is not hygroscopic;

1. Will not run or tend to water-break;

g. Can withstand high pouring temperatures and produce an exceptionally smooth finish on the surface of the casting adjacent the core; and

h. Utilizes commercially available and economical ingredients.

Other objects and advantages of the invention will appear from the following description forming a part of the specification.

Basically the core coating composition herein devised comprises as essential ingredients, magnesium oxide, magnesium chloride, calcium oxide, graphite and water. The

graphite is preferably in the form of flakes and the water is to be of an amount to produce the desired Baum.

The relative proportions of the essential ingredients which may 'be employed based on 100% with water to be added are:

Concentration, percent Calcium oxide 22.3-23 Magnesium chloride 5.65-5.67 Magnesium oxide 3.753.95 Graphite 67.25-68.6

As a specific example of ingredients by weight a preferable composition would include 6 lbs. of magnesium oxide, 9 lbs. of magnesium chloride, 36 lbs. of calcium oxide, and 108 lbs. of graphite. By percentage totaling 100% the ingredients are as follows:

Percent Magnesium chloride 5.66 Magnesium ox e 3.77 Calcium oxide 22.65 Graphite 67.92

The proportionate weight of the magnesium chloride and magnesium oxide is very important since these mgredients upon drying combine to form magnesium oxychloride. The oxyehloride as such both hardens and binds the coating. Whereas a slight excess of magnesium oxide would cause little change, an excess of magnesium chloride would have no magnesium oxide to combine with and would thus crystallize out on drying.

An allowable variation from the example by weight hereinbefore set forth permits of the addition of 4 ounces to the 6 lbs. of magnesium oxide, maintaining the magnesium chloride at 9 lbs., increasing or decreasing the 36 lbs. of calcium oxide by /5 lb. and increasing or decreasing the 108 lbs. of graphite by 1 lb. Any increase or decrease of calcium oxide or graphite beyond the aforesaid stated limits would tend to make a permeable coating that would tend to water-break or run. Water is added to the composition in amounts to provide a Baum of between 30 and 50.

The compositions may be applied in dilute aqueous form to the surface of dry sand cores by dipping, spraying or brushing, as desired. The sand cores which may be improved by such treatment include sand cores fabricated in accordance with conventional foundry practice using core oil or resin bonded sand cores made by the shell molding process. No disadvantage in use or in compatibility has been observed between the ingredients of the compositions of this invention and the fully polymerized constituents of the sand cores manufactured by the shell mold process.

The compositions of this invention may be formulated and applied to sand cores in a variety of specific ways. Reference is had to our copending application Serial No. 297,575 as to a specific manner of formulating the composition and for applying it to the core to be coated. Preferably the ingredients are uniformly admixed in suitable apparatus such as a rotary mixer and then mixed with water to a viscous concentrate. Subsequently the concentrate is diluted to the desired consistency such as between 30 and 55 Baum whereupon it is suitable for application, preferably by spraying, to the core to be coated. The spraying or other manner of application is carried out under elevated temperatures of the core whereupon a uniform smooth coating is produced on the core.

With the core so coated gray iron articles in permanent molds can be cast at temperatures of between 2700 and 2800 producing a surface on the articles adjacent to the core which are smooth and free from bubbles or pock marks.

The compositions of this invention are sufliciently heat resistant to withstand metal pouring temperatures in excess of 3000 without any disruption of the coating from the inflow of molten metal since they were devised primarily for use in gray iron casting. Although primarily adaptable to gray iron castings the coating compositions are not to be limited to such application since it is conceivable that they are equally suitable for casting alloy steels or other like metals. Accordingly, the invention is to be interpretated in the light of the disclosures made as defined by the appended claims.

What we claim is:

1. A sand core coating composition consisting essentially of the following proportions by weight, 9 parts of magnesium chloride, 6 to 6% parts of magnesium oxide, 35 to 36 /2 parts of calcium oxide, 107 to 109 parts of graphite and sutlicient water to produce a desired Baum of between 30 and 55.

2. A sand core coating composition consisting essentially of the following proportions by weight, 9 parts of magnesium chloride, 6 parts of magnesium oxide, 36 parts of calcium oxide, 108 parts of graphite and sufficient water to produce a desired Baum of between 30 and 55.

3. A sand core coating composition for use in conjunction with permanent molds which comprises an aqueous mixture including essentially solid ingredients totaling 100% by weight proportioned as follows: 5.65% to 5.67% magnesium chloride, 3.75% to 3.95% magnesium oxide, 22.3% to 23% calcium oxide, and 67.25% to 68.6% graphite, and water in sufiicient amount to produce a desired Baum of between 30 and 55.

4. A sand core coating composition comprising an aqueous mixture of a desired Baum of between 30 and 55 for use in conjunction with gray iron casting or the like, including water and solid ingredients with the solid ingredients based on 100% total by weight aside from the water proportioned as follows: 5.66% magnesium chlo- 4 ride, 3.77% magnesium oxide, 22.65% calcium oxide, and 67.92% graphite.

5. A sand core having on the surface thereof a dried continuous smooth refractory coating consisting essentially by weight of, approximately 36 parts of calcium oxide, 9 parts of magnesium chloride, 6 parts of magnesium oxide and 108 parts of graphite.

References Cited in the file of this patent UNITED STATES PATENTS 53,092 Sorel Mar. 6, 1866 100,944 Sorel Mar. 15, 1870 223,565 Webb Jan. 13, 1880 468,292 Cole Feb. 2, 1892 711,329 Mielck Oct. 14, 1902 720,142 Heuber Feb. 10, 1903 1,096,384 Morris May 12, 1914 1,811,799 Lukens June 23, 1931 1,861,592 Beck June 7, 1932 

1. A STAND CORE COATING COMPOSITION CONSISTING ESSENTIALLY OF THE FOLLOWING PROPORTIONS BY WEIGHT, 9 PARTS OF MAGNESIUM CHLORIDE, 6 TO 61/4 PARTS OF MAGNESIUM OXIDE, 351/2 TO 361/2 PARTS OF CALCIUM OXIDE, 107 TO 109 PARTS OF GRAPHITE AND SUFFICIENT WATER TO PRODUCE A DESIRED BAUME'' OF BETWEEN 30% AND 55*. 